Light Emitting Device

ABSTRACT

This disclosure relates to a light-emitting apparatus comprising a submount, a chip carrier formed on the submount, a light-emitting chip formed on the chip carrier, a reflecting cup formed on the submount and enclosing the light-emitting chip and the chip carrier, and a transparent encapsulating material for encapsulating the light-emitting chip.

REFERENCE TO RELATED APPLICATION

The present application claims the right of priority based on TaiwanApplication Serial Number 095126899, filed Jul. 21, 2006, the disclosureof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This invention relates to a light-emitting chip, and a light-emittingapparatus comprising the light-emitting chip.

BACKGROUND OF THE DISCLOSURE

Light extraction efficiency of light-emitting diodes (LEDs) has becomean important topic in improving brightness. A variety of conventionalskills has been focused on the research of the surface roughening of LEDchips for increasing the light extraction efficiency of LED chips. Forexample, texturing the top or bottom surface of the substrate by wetetching or dry etching for improving the scattering effect of thesubstrate, or roughening the top surface of the epitaxial structure byetching or growth method such that more light can be extracted from thetop side of the LED chip have been tried to improve the light extractionefficiency of LED chips themselves. In addition, an adapted package formalso plays a role in helping LED chips to achieve excellent lightextraction efficiency.

FIG. 1 shows an conventional SMD (Surface Mount Device) type LEDapparatus 10 comprising a submount 11 having a first conductive line 111and a second conductive line 112, an LED chip 13 formed on the centralportion of the submount 11, a reflecting cup 12 formed on the submount11 and enclosing the LED chip 13, and a transparent encapsulatingmaterial 14 filled in the cavity formed by the reflecting cup 12 forencapsulating the LED chip 13. The light-emitting chip 13 comprises afirst electrode (not shown) and a second electrode (not shown)electrically connected to the first conductive line 111 and the secondconductive line 112 correspondingly by separate wires 19. The firstconductive line 111 and the second conductive line 112 are extended fromthe top surface to the bottom surface of the submount 11 for mounting ona printed circuit board (PCB). The reflecting cup 12 redirects the lightemitted from the LED chip 13 upwardly to form a directional light beam.Having the whole cavity filled with the transparent encapsulatingmaterial 14, part of the light is not able to transmit through thetransparent encapsulating material 14 due to the total reflection at theinterface between the transparent encapsulating material 14 and theambient surroundings. Besides, it is difficult to dissipate the heatgenerated from the LED chip 13 through the reflecting cup 12.

U.S. Patent Publication No. US2005/0067628 proposes a way to overcomethe abovementioned problems. As shown in FIG. 2, a transparentencapsulating material 24 encapsulates only an LED chip 23 such that themajority of light is able to pass through the transparent encapsulatingmaterial 24, and the probability of total reflection is significantlylowered. However, part of light is still confined within the reflectingcup. Moreover, spaces are formed between the reflecting cup 22 and a cupsupporter 221 for disposing some peripheral electronic elements and itis difficult to dissipate the heat generated from the LED chip 23through the reflecting cup 22.

In view of the above, the invention proposes a light-emitting apparatusfor improving the light extraction efficiency and the heat dissipation.

SUMMARY OF THE DISCLOSURE

One aspect of the invention proposes a light-emitting apparatus having achip carrier formed between an LED chip and a submount. Thelight-emitting apparatus comprises a submount having a first conductiveline and a second conductive line, a chip carrier formed on thesubmount, an LED chip formed on the chip carrier, a reflecting cupformed on the submount and enclosing the LED chip and the chip carrier,and a transparent encapsulating material encapsulating the LED chip. TheLED chip comprises a first electrode and a second electrode electricallyconnected to the first conductive line and the second conductive line byseparate wires.

In one embodiment, the ratio of the height of the chip carrier to theheight of the reflecting cup is within a predetermined range.

In another embodiment, the chip carrier is integrally formed as a partof the LED chip or the submount.

Another aspect of this invention proposes a chip unit having a chipcarrier. The chip unit further comprises a growth substrate formed onthe chip carrier, a light-emitting stack formed on the growth substrate,a first electrode and a second electrode electrically connected to thelight-emitting stack.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a light-emitting apparatus according to one prior art.

FIG. 2 shows a light-emitting apparatus according to another prior art.

FIG. 3 shows a light-emitting apparatus according to the firstembodiment of the present invention.

FIG. 4 demonstrates the simulation result of the correlation curve ofthe height of the chip carrier versus the light extraction efficiency.

FIG. 5 shows a light-emitting apparatus according to the secondembodiment of the present invention.

FIG. 6 shows a light-emitting apparatus according to the thirdembodiment of the present invention.

FIG. 7 shows a chip unit according to one embodiment of the presentinvention.

FIG. 8 shows a light-emitting apparatus comprising a light-convertinglayer according to one embodiment of the present invention.

FIG. 9 shows a light-emitting apparatus comprising a light-convertinglayer according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 shows one embodiment according to the present disclosure. Alight-emitting apparatus 30 comprises a submount 31 having a firstconductive line 311 and a second conductive line 312, a chip carrier 35formed on the submount 31, an LED chip 33 formed on the chip carrier 35,a reflecting cup 32 formed on the submount 31 and enclosing the LED chip33, and a transparent encapsulating material 34 filled in the cavityformed by the reflecting cup 32. The LED chip 33 comprises a firstelectrode (not shown) and a second electrode (not shown) electricallyconnected to the first conductive line 311 and the second conductiveline 312 by separate wires 39. The first conductive line 311 and thesecond conductive line 312 are extended from the top surface to thebottom surface of the submount 31 for mounting on a printed circuitboard (PCB). The reflecting cup 32, the submount 31, and/or the chipcarrier 35 comprise a reflecting surface or a reflecting layer (notshown) formed thereon for redirecting the light emitted from the LEDchip 33 upwardly to form a directional light beam. The reflecting layercomprises at least one material selected from the group consisting ofsilver, aluminum, silicon oxide, and aluminum oxide. The chip carrier35, the submount 31, and the reflecting cup 32 can be formed integrallyor separately. It is preferred that the chip carrier 35 can be bonded tothe submount 31 by an adhesive layer. The adhesive layer comprises atleast one material selected from the group consisting of metal, metalalloy, eutectic metal alloy, silver paste, polyimide, benzocyclobutene(BCB), perfluorocyclobutane (PFCB), epoxy resin, and silicone. Thebonded structure is advantageous for dimension tuning. Moreover, itenhances the light extraction efficiency by matching the LED chip andthe reflecting cup to a chip carrier with an appropriate height.

FIG. 4 shows the effect of the height of the chip carrier to the lightextraction efficiency according to the present disclosure. Please alsorefer to FIG. 3, the exemplified dimensions of the light-emittingapparatus 30 are measured and described subsequently. The height of thereflecting cup 32 is 1 mm, the height of the LED chip 33 is 95 um, thedimension of the LED chip 33 is 380 um by 380 um, the forming angle θbetween the reflecting cup 32 and the submount 31 is about 80 degree,and the top area of the height of the chip carrier 35 is about 500 um by500 um. The light extraction efficiency can be enhanced by controllingthe carrier height from 50 um to 400 um, i.e. the ratio of height of thechip carrier h to the height of the reflecting cup H is about 0.1 to0.4. To further improve the light extraction efficiency, it isachievable to fine tune those dimensions, such as the forming angle θ,the ratio of the width of the LED chip and that of the reflecting cup(or the width of the submount) for better performance.

FIG. 5 shows another embodiment according to the present disclosure. Alight-emitting apparatus 50 comprises a submount 51 having a firstconductive line 511 and a second conductive line 512 extended from thetop surface to the bottom surface of the submount 51, a chip carrier 55formed on the submount 51, an LED chip 53 formed on the chip carrier 55,a reflecting cup 52 formed on the submount 51 and enclosing the LED chip53 and the chip carrier 55, and a transparent encapsulating material 54encapsulating only the LED chip 53 and the chip carrier 55. The LED chip53 comprises a first electrode (not shown) and a second electrode (notshown) electrically connected to the first conductive line 511 and thesecond conductive line 512 by separate wires 59. The reflecting cup 52,the submount 51, and/or the chip carrier 55 comprise a reflectingsurface or a reflecting layer (not shown) formed thereon. The reflectinglayer comprises at least one material selected from the group consistingof silver, aluminum, silicon oxide, and aluminum oxide. The reflectingcup 52 and/or the chip carrier 55 comprise a material having a highthermal conductivity, such as silicon, aluminum, copper, or silver, forconducting the heat generated by the LED chip 53 into the atmosphere bythe reflecting cup 52. The chip carrier 55, the submount 51, and thereflecting cup 52 can be formed integrally or separately. Since thetransparent encapsulating material 54 encapsulates only the LED chip 53and the chip carrier 55 instead of filling the whole cavity formed byreflecting cup 52, the light extraction efficiency can be furtherimproved.

FIG. 6 shows another embodiment according to the present invention. Alight-emitting apparatus 60 comprises a submount 61 having a top andbottom surface, a first conductive line 611 and a second conductive line612 extended from the top surface to the bottom surface of the submount61, a chip carrier 65 formed on the submount 61, an LED chip 63 formedon the chip carrier 65, a reflecting cup 62 formed on the submount 61and enclosing the LED chip 63 and the chip carrier 65, and a transparentencapsulating material 64 encapsulating only the LED chip 63 and thechip carrier 65. The LED chip 63 comprises a first electrode (not shown)and a second electrode (not shown) electrically connected to the firstconductive line 611 and the second conductive line 612 by separate wires69. The reflecting cup 62, the submount 61, and/or the chip carrier 65comprise a reflecting surface or a reflecting layer (not shown) formedthereon. The reflecting layer comprises at least one material selectedfrom the group consisting of silver, aluminum, silicon oxide, andaluminum oxide. A transparent stand 66 is formed on the submount 61 andencloses the LED chip 63 for confining the transparent encapsulatingmaterial 64 adjacent to the LED chip 63 and preventing the transparentencapsulating material 64 from out-spreading which will adverselyaffects the curvature of the transparent encapsulating material 64. In apreferred embodiment, the transparent stand 66 is not higher than thechip carrier 65 in order to keep the shape of the transparent stand 66to be substantially hemisphere. In a preferred embodiment, the chipcarrier 65 can be integrally formed as a part of the submount 61.

FIG. 7 shows one embodiment of a chip carrier 71 being integrally formedas a part of a chip unit 70. The chip unit 70 can be bonded to asubmout. The chip unit 70 having the chip carrier 71, further comprisesa growth substrate 72 bonded to the chip carrier 71 by an adhesive layer76, a light-emitting stack 73 formed on the growth substrate 72, a firstelectrode, and a second electrode electrically coupled to thelight-emitting stack 73. The chip carrier 71 comprises a material havinghigh thermal conductivity, such as silicon, aluminum, copper or silver.The adhesive layer 76 comprises at least one material selected from thegroup consisting of silver paste, polyimide, benzocyclobutene (BCB),perfluorocyclobutane (PFCB), epoxy resin, and silicone. The growthsubstrate 72 comprises at least one material selected from the groupconsisting of sapphire, GaN, glass, GaP, SiC, and CVD diamond. Thelight-emitting stack 73 emits light when driving under a voltage bias.The color of light depends on the material system of the light-emittingstack 73. For example, (Al_(p)Ga_(1-p))_(q)In_((1-q))P series will emitreddish, yellowish, or greenish light depending on the value of p, q;whereas Al_(x)In_(y)Ga_((1-x-y))N series will emit bluish, or violetlight depending on the value of x, y. The light-emitting stack 73comprises a first semiconductor layer 731 of first conductivity-type, asecond semiconductor layer 733 of second conductivity-type opposite tothe first conductivity-type, an active layer 732 interposed between thefirst semiconductor layer 731 and the second semiconductor layer 733.The structure of the active layer 732 can be double-heterojunction (DH)or multi-quantum well (MQW) for higher internal quantum efficiency.Although FIG. 7 depicts a lateral structure of the first electrode 74and the second electrode 75 on the same side with respect to the growthsubstrate 72, it is still under the scope of the invention, for thoseskill in the art to modify the chip unit 70 in accordance with thepresent invention to be a vertical-type form.

FIG. 8 exemplifies one embodiment according to the present invention forconverting the light emitted by an LED chip 83 into white or othervisible light via a light-converting layer 87 conformably coated on thesurface of a reflecting cup 82 and a submount 81. The light-convertinglayer 87 comprises the well-known phosphor materials, such as YAG, TAG,oxy-nitride compound, or silicate compound. The light-emitting stack ofthe LED chip 83 comprises GaN or AlGaInP. It is also preferred to formthe light-converting layer 97 adjacent to the top region of thereflecting cup in a remote-coating fashion.

It should be noted that the proposed various embodiments are not for thepurpose to limit the scope of the invention. Any possible modificationswithout departing from the spirit of the invention may be made andshould be covered by the invention.

What is claimed is:
 1. A light-emitting device, comprising: a submounthaving a upper surface, a lower surface, and a side boundary; an LEDchip; a chip carrier arranged between the upper surface and the LEDchip; a first conductive line penetrating the submount, and having afirst end electrically connected to the LED chip and a second endexposed on the lower surface without touching the side boundary; and alight converting layer covering the LED chip and the chip carrierwithout directly contacting the LED chip.
 2. The light-emitting deviceof claim 1, further comprising a transparent material covering the LEDchip without directly contacting the light converting layer.
 3. Thelight-emitting device of claim 1, further comprising a second conductiveline electrically connected to the LED chip and penetrating the submountwithout covered by the LED chip or the chip carrier.
 4. Thelight-emitting device of claim 3, wherein the chip carrier is arrangedbetween the first conductive line and the second conductive line.
 5. Thelight-emitting device of claim 1, further comprising a bonding layerarranged between the LED chip and the chip carrier.
 6. Thelight-emitting device of claim 1, further comprising a reflecting layerformed on the chip carrier and being wider than the LED chip.
 7. Thelight-emitting device of claim 1, wherein the second end is wider thanfirst end.
 8. The light-emitting device of claim 1, wherein the LED chipcomprises a first electrode having a width substantially equal to thatof the first end.
 9. The light-emitting device of claim 1, wherein thelight converting layer is arranged in a configuration that any part ofthe submount is lower than the light converting layer.
 10. Thelight-emitting device of claim 1, wherein the first end is not coveredby the LED chip or the chip carrier.
 11. The light-emitting device ofclaim 1, wherein the light converting layer is substantially connectedto the side boundary.